1. Field of Invention
The present invention relates to semiconductor device manufacturing and, in particular, to apparatuses and methods for chemical-mechanical polishing of semiconductor wafers.
2. Related Art
FIG. 1 is a side view of a conventional chemical-mechanical polishing (CMP) apparatus used, for example, to planarize the device surface of a processed semiconductor wafer during device fabrication. Circular platen 10 is shown connected to platen drive 12 through shaft 14. Platen drive 12 causes platen 10 to rotate during polishing operations. Polishing pad 16 is shown mounted on platen 10 top surface 18. The top surface of pad 16 is polishing surface 20. Pad 16 is typically felt or urethane with a foam backing, or a material having an abrasive embedded in surface 20.
Also shown is a conventional wafer carrier 22 positioned over platen 10. Carrier 22 is attached to carrier drive 24 through shaft 26. Carrier 22 holds device surface 28 of processed semiconductor wafer 30 against polishing surface 20 during polishing. During some conventional polishing operations, carrier drive 24 causes carrier 22, and hence wafer 30, to rotate against polishing surface 20. In other conventional polishing operations, carrier drive 24 causes carrier 22, and hence wafer 30, to translate laterally across polishing surface 20. In some apparatuses drive 24 may cause simultaneous rotational and translational motion of carrier 22.
Slurry reservoir 32 supplies conventional polishing slurry 34 to polishing surface 20 using conventional slurry delivery system 36. Slurry 34 may be an abrasive carried in a fluid suspension, a compound formulated to have a chemical effect on device surface 28, or a combination of both. Platen 10's rotation causes slurry 34 to flow radially outward across polishing surface 20, thus creating a thin layer (not shown) of polishing slurry on surface 20. Delivery system 36 typically includes pumps and tubing (not shown).
During conventional chemical-mechanical polishing, slurry 34 is dispensed at a fixed flow rate onto polishing surface 20. Wafer 30 is mounted to carrier 22 which is then positioned to place device surface 28 against polishing surface 20. Platen 10 and carrier 22 are rotated and, as additional slurry 34 is introduced, the desired polishing effect on device surface 28 is obtained. When polishing is completed, carrier 22 is removed from polishing surface 20 and wafer 30 is removed from carrier 22. A new wafer may then be mounted on carrier 22, and the polishing process is repeated.
The polishing operation adversely affects polishing surface 20. The pressure of device surface 28 against polishing surface 20 typically deforms surface 20's fine surface structure. Therefore, a conditioner is typically used either during or after polishing so as to keep surface 20 in a near pristine state. The conditioner is typically a compound of diamonds that are bonded to a substrate. The bonded diamonds and substrate are then nickel plated, and the combination is used to clean and roughen the polishing pad surface. The conditioning process is difficult to optimize, however, and consequently it is difficult to keep polishing surface 20 in the required state for proper polishing. What is required is a chemical-mechanical polishing apparatus and process in which the polishing surface is easily kept in a near optimum state for polishing.